### Please describe the problem.

I added a YT vid via addurl and then intentionally corrupted it by rewriting the underlying contents. After doing so, the video was clearly broken, but `git annex fsck` did not detect this.


### What steps will reproduce the problem?

```
$ git annex addurl 'https://www.youtube.com/watch?v=zGDzdps75ns'
addurl https://www.youtube.com/watch?v=zGDzdps75ns 
(using yt-dlp) (to Small short test video [zGDzdps75ns].webm) 
ok                                   
(recording state in git...)
$ git commit -m 'test'
$ echo test | sudo tee './Small short test video [zGDzdps75ns].webm'
test
$ git annex fsck './Small short test video [zGDzdps75ns].webm'
fsck Small short test video [zGDzdps75ns].webm ok
(recording state in git...)
$ file -L ./Small\ short\ test\ video\ \[zGDzdps75ns\].webm
./Small short test video [zGDzdps75ns].webm: ASCII text
```

The fsck reports the file is "ok". Even an fsck `--from=web` reports the video is OK:

```
$ git annex fsck './Small short test video [zGDzdps75ns].webm' --from=web
fsck Small short test video [zGDzdps75ns].webm 
ok                                    
(recording state in git...)
```

In contrast, doing the same thing to a non-youtube video via addurl _does_ get detected by fsck:

```
$ git annex addurl 'https://git-annex.branchable.com/logo_small.png'
addurl https://git-annex.branchable.com/logo_small.png 
(to git-annex.branchable.com_logo_small.png) ok
(recording state in git...)
$ git commit -m 'test'
$ echo test | sudo tee ./git-annex.branchable.com_logo_small.png 
test
$ git annex fsck ./git-annex.branchable.com_logo_small.png
fsck git-annex.branchable.com_logo_small.png 
  git-annex.branchable.com_logo_small.png: Bad file size (4.74 kB smaller); moved to .git/annex/bad/SHA256E-s4749--c604d942bd8edebe5e8e01d18d1ad3604b0874c38d436c9486c52d601e4251dd.png
failed
(recording state in git...)
fsck: 1 failed
```



### What version of git-annex are you using? On what operating system?

10.20230828, on Ubuntu Jammy.


### Please provide any additional information below.

[[!format sh """
# If you can, paste a complete transcript of the problem occurring here.
# If the problem is with the git-annex assistant, paste in .git/annex/daemon.log


# End of transcript or log.
"""]]

### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)

Excited to move my photo collection over to it!


